Today's increasing use of and reliance on communications networks has led to the development of new standards and protocol that provide more reliable and efficient network services to consumers.
A standard that is still developing is MPLS (Multi-Protocol Label Switching). This emerging standard allows packets or any data transmission units (DTUs) to be routed in the MPLS network based simply on a label that the DTU is carrying. This process facilitates the complexity of route lookups that are based on a destination IP (Internet Protocol) address. Thus, a DTU (Data Transmission Unit) arriving at a router is forwarded to another router based merely on the a DTU's label. At the next router, the label of the DTU may be replaced or added to for the next “hop” in the DTU's travel towards its ultimate destination. While the MPLS standard promises great benefits, very few methods have been developed for fault detection/management of an MPLS network.
One solution to the above need has been suggested by ITU-T Y.1711. In this document, discussed is the use of a special Operation And Maintenance (OAM) packet that can be used to determine the performance of an MPLS network. An unused reserved MPLS label value is used at the bottom of the label stack of OAM packets to delineate OAM packets for transport between Label Switch Path (LSP) ingress and egress points. This approach, unfortunately, only allows for performance determination between these ingress and egress points. The performance of network segments between these ingress and egress points is not possible nor even considered in the above proposal. Furthermore, the use of a specific MPLS label value for OAM packets leads to increased overhead costs for this proposal.
By way of explanation, it should be noted that an LSP is a specific data traffic path in an MPLS network. Such LSPs are provided for by LDPs (Label Distribution Protocols) that establish these paths and reserves the necessary resources on the nodes in the path to meet predefined service requirements of the data path. An LSP is analogous to the route that a packet or DTU is tasked to follow in being transmitted from an ingress (entry) LSP node to an egress (exit) LSP node. LSPs are established from the egress LSP node to the ingress LSP node. As such, the egress LSP node uses LDP to distribute the relevant labels to the relevant nodes. Once a DTU arrives at the ingress LSP node, the DTU is thus forwarded to the egress LSP node based on the forwarding decisions dictated by the distributed labels.
An LDP is a specification that allows a label switch router (LSR) to distribute labels to its LDP peers. In MPLS, since DTUs are routed based on the labels carried by the DTUs, the routers (LSR) must know where to route the DTUs based on the labels carried by the DTU. Thus, if an LSR assigns a label A to a class of DTUs, that LSR must notify the other LSRs of the meaning of that label A (i.e. what to do or how to process or route a DTU with label A). This is accomplished by using an LDP. Since a set of labels from the ingress LSR (entry router) to the egress LSR (exit router) in an MPLS network defines a Label Switched Path (LSP), LDPs help in establishing an LSP by using a set of procedures to distribute the labels among the LSP peers (i.e. the ingress LSP and the egress LSPs are peers in that they communicate with each other at the same level—they can change what each has done).
From the above discussion, any solution to the above performance determination problem should ideally make use of the existing infrastructure that adheres to the MPLS standard. Such a solution would not require increased logic to be implemented and should allow for segmentation of LSPs in terms of performance and fault isolation.
It should be noted that the term data transmission unit (DTU) will be used in a generic sense throughout this document to mean units through which digital data is transmitted from one point in a network to another. Thus, such units may take the form of packets, cells, frames, or any other unit as long as digital data is encapsulated within the unit. Thus, the term DTU is applicable to any and all packets and frames that implement specific protocols, standards or transmission schemes. It should also be noted that the term digital data will be used throughout this document to encompass all manner of voice, multimedia content, video, binary data or any other form of data or information that has been digitized and that is transmitted from one point in a network to another as a payload of a data transmission unit.